Mobile Phones
Radio phones have been around for a while. The first mobile telephone
call was made September 11, 1946 between a Houston Post and a St. Louis Globe
reporter. An old mobile phone service in New York city had 700 subscribers,
but could only handle 12 conversations at a time (because it had 12 channels).
There are some 160,000 mobile telephones nationwide.
The old service was doomed to fail. Each major city had one or two
powerful transmitters to communicate with all car phones in a 30- to 50-mile
radius. To make a call from a car, you must find a vacant channel, then call
the operator and supply the number you want to call. The operator dials the
number and connects you when the party answers. Only a few companies have dial
it yourself service. If someone wants to call you, they must first find the
mobile phone operator in your area. The operator finds a vacant channel and
transmits a series of tones that correspond to your phone and make it ring-sort
of as if it were a pager. Once you answer, the operator connects you and the
caller.
Clearly, the system was slow. Worse, it could only serve a few users at a
time. During rush hour, there was little hope of making a call. Few channels
could be added because of the dearth of frequencies for that kind of operation.
So now you can't get a mobile phone of this type unless someone else gives one
up.
Enter the cellular mobile radio. Instead of only 1 or 2 transmitters, an
area is divided up into many small sections, called 'cells'. Wach has it's own
low-powered transmitter just strong enough to serve it's cell. An average cell
covers from one to eight square miles and varies in shape from a circle to a
squashed football. Each cell touches another, some overlap slightly.
Adjacent cells use different channels-there are more than 600 in each city
to choose from-and a channel may be reused several times in the city if the
cells are located far enough apart. All of the cells' transmitters hook into
one network switching office, much like a central office handles calls form lan
d-based telephones.
Each transmitter constantly sends out a special signal, and as you drive
from cell to cell, your telephone automaticly tunes in the strongest cell. When
a call comes in for you, the network switching office uses the channel to send
a digital pulse signal that corresponds to your ten-digit phone number (NPA+7 d
igits).
When the phone hears it's number, it in effect says 'Here I am, in this
certain cell'. That information is sent back to the network switching office,
which scans vacant frequencies, and relays the information to your cell.
Finally, your unit tunes to that voice channel, and the cell site rings you,
and you talk.
It sounds complicated-and it is. But it works in seconds. And it can be
expanded. As more and more phones are added, cells can be split into smaller
cells with less power. Cellular radio allready exists in Japan, Denmark,
Norway, and Sweden. In Denmark, service began in 1981 and grew to 100,000
customers almost overnight. Within a few years all of Scandinavia will have
compatable cellular systems. Australia, Canada, and Mexico also plan systems.
Why has the U.S. lagged behind? Yep, it's our old freinds, the FCC. They
studied the system for 12 years before okaying the service in 1982. The U.S.
may be fullt celled by 1988. Now is the time to rent your backyard as a
cellular station!
The Bell companies will operate cellular service as the Cellular Service
Company. Others such as GTE and MCI plan similar service. Even the Washington
Post is trying to get into it. There are allready two systems, one in
Washington/Baltimore, and one in Chicago. Chicago users pay about $50 rent and
$25 monthly use fee for 120 minutes, and 25 cents/minute hereafter. Average
bills are $150/month.
The main unit mounts in the trunk, and just the handset sits up front. The
antennas are very small-about nine inches-and are hidden inside the car.
Now freaking old car phone systems shoudln't be that hard if you really
try. The following are the freq's to remember:
158.07-158.49 MHz (mobile)
152.81-153.03 MHz (base stations)
You CAN listen in on these freq's. What I'm not sure about is whether you can
place a call --I would think so. So Freq out!
COMMING SOON: Repair trucks, installers, and linesmen, Marine Radio, and
Airplane phones
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